How do I upgrade my Yamaha 9.9 2 stroke to 15 hp?

[mbackc]

Dear all.

Im in doubt whether I can upgrade my Yamaha 9.9 2 stroke engine to a 15 hp. How can I determine whether the reed valve / reed housing is a 9.9 or 15hp ? I have read that the carb is the same. The previous owner mentioened that it might have already been upgraded but he wasnt sure. One thing I have noticed is that the engine only increases the RPM up to half throttle or 2/3 throttle. After that point it runs smooth but is seems like there is potential for more.

Do anyone know how to determine the difference between 9.9 & 15 inlet parts ? Please take a look at the attached photos. Seems like the max movement / opening of the reed valve is approximately 6-7mm.

Last but not least which parts is needed if I can upgrade ? Part numbers are welcome...

Hope someone can assist.

Thanks for your kind assistance in advance.

All the best.

Michael Back
Copenhagen - Denmark

 

[Scott Danforth]

the easiest way to convert your motor is as follows:

sell 10hp, converting motor to pile of cash
open wallet, dump contents of wallet onto pile of cash, making the pile of cash slightly bigger
take slightly bigger pile of cash and buy bigger motor. (converting the cash to a 15hp motor

that being said. if your 9.9 shares the exact same power head (not just the block casting) with a15hp, it may be feasible. however you're going to have to compare the parts breakdown of both motors. many times its the block casting and crank that are common with different machining on the blocks and different pistons, carb, etc. a few have been a carb and restrictor plate